Black Holes Hidden in Dark Matter Halos
This presentation explores how rotating black holes behave when surrounded by pseudo-isothermal dark matter halos. Using the Newman-Janis algorithm to extend spherical solutions to rotating systems, the researchers investigate the effects on event horizons, photon orbits, and black hole shadows. Remarkably, they find that dark matter density has minimal impact on observable shadow properties, a finding with important implications for interpreting Event Horizon Telescope observations of supermassive black holes like M87.Script
Supermassive black holes sit at the centers of galaxies, wrapped in invisible dark matter halos that outweigh all visible stars combined. But when we photograph a black hole's shadow, does that dark matter change what we see?
The researchers model a rotating black hole surrounded by a pseudo-isothermal dark matter halo, a profile that avoids the unrealistic density spikes of simpler models. Their target is understanding M87, the supermassive black hole we've actually photographed, to see if dark matter leaves observable traces.
They need a rotating solution, not just a static sphere.
The authors derive the spherical black hole metric with the dark matter halo, then apply the Newman-Janis algorithm to add spin. This transforms the static solution into a rotating one, letting them trace how photons travel through the warped spacetime to form shadows.
Here's the surprise. While increasing spin dramatically shrinks the gap between inner and outer event horizons, the dark matter halo barely changes anything. The shadow we observe depends almost entirely on the black hole's rotation, not the invisible matter surrounding it.
This means the stunning black hole images from the Event Horizon Telescope are showing us the black hole itself, not its dark matter shroud. To detect the halo's influence, the authors suggest gravitational wave astronomy might be the key, where subtle differences in spacetime ripples could reveal what shadows cannot.
Dark matter may dominate the universe's mass, but when it comes to black hole portraits, the star of the show is gravity itself. To explore more cutting-edge research like this and create your own videos, visit EmergentMind.com.
